bioRxiv preprint doi: https://doi.org/10.1101/2020.09.09.289918; this version posted September 10, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Free-living marine nematodes diversity at Ponta Delgada-São Miguel (Azores archipelago, North-East Atlantic Ocean): first results from shallow soft-bottom habitats Alberto de Jesús Navarrete1*, Víctor Aramayo2,3, Anitha Mary Davidson4. Ana Cristina Costa5 1 Systematic and Aquatic Ecology Department, El Colegio de la Frontera Sur, Unidad Chetumal, México. Av. Centenario km 5.5, Chetumal Quintana Roo, México. 2 Facultad de Ciencias Biológicas, Universidad Nacional Mayor de San Marcos, P.O. BOX 1898, Lima 100, Peru. 3 Dirección de Oceanografía y Cambio Climático. Instituto del Mar del Perú, P.O. BOX 22, Callao, Peru. 4 School of Ocean Studies and Technology, Kerala University of Fisheries and Ocean Studies, Panangad PO Kochi 682506, Kerala India. Present address: CSIR-National Institute of Oceanography, Regional Centre, Kochi-682018, Kerala India. 5 Faculdade de Ciências e Tecnologia e CIBIO/InBio – Centro de Investigação em Biodiverdade e Recursos Genéticos, Universidade dos Açores * Corresponding author: [email protected] bioRxiv preprint doi: https://doi.org/10.1101/2020.09.09.289918; this version posted September 10, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Abstract Contrasting (sand, algae, rocky-dominated, mixed) benthic habitats were sampled to characterize marine nematode diversity inhabiting surface sediments in São Miguel (Azores, North-East Atlantic Ocean) in July 2019. Nematodes were extracted from the surface layer of sediments and morphologically identified using light microscopy. Nematode taxonomy was based on living/fresh specimens) to ensure a suitable recognition of morphological traits. Our results provide a preliminary checklist of free-living marine nematode genera from 21 intertidal and sublittoral sandy beach sites along the coast of São Miguel island, Azores archipelago, Portugal. The nematode fauna was represented by 4 orders, 21 families, and 43 genera. Cyatholaimus, Desmodora and Daptonema had two morphospecies each. Enoplida was represented by 8 families and 13 genera, while Chromadorida by 7 families and 18 genera, the latter corresponding to the most diverse nematode group. Monhysterida had 5 families and 10 genera and Araeolaimida was represented by a single 1 family and 2 genera. The most common genera (i.e., accounting for 75% of all organisms) included Adoncholaimus (most abundant genus, 32 specimens), Axonolaimus (18), Cyatholaimus (17), Enoploides (13), Rhabdocoma, and Acanthopharynx (11). Viscosia and Enoplolaimus were represented by 7 specimens, whilst Halalaimus, Desmoscolex, Monophostia, Daptonema, and Theristus obtained only 6 each. The dominant nematode taxa of São Miguel island have been commonly previously reported in other coastal habitats including sandy beaches. They can be considered typical meiofaunal components of intertidal sandy beaches. Many of the nematode morphotypes found in São Miguel island could represent new species to science. As far as we know, this is the first report on free-living nematodes for São Miguel Island and for marine shallow water in the Azores. Our findings will serve as an import baseline for future research aiming to improve our understating of nematode communities in volcanic islands such as São Miguel in the Azores archipelago. Keywords: free-living marine nematodes, meiofauna, intertidal benthic habitats, volcanic sediments. bioRxiv preprint doi: https://doi.org/10.1101/2020.09.09.289918; this version posted September 10, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Resumo Diversos habitats bentónicos (areia, algal, rochoso e misto) foram amostrados para caracterizar a diversidade de nematodes marinhos que habitam o sedimento superficial em São Miguel (Açores, Oceano Atlântico Nordeste) em Julho 2019. Os nematodes foram extraídos da camada superficial de sedimento e identificados morfologicamente usando microscopia óptica. A identificação taxonómica realizou-se com base na observação de especímenes vivos e/ou frescos para garantir o reconhecimento adequado dos caracteres morfológicos. Os resultados providenciam uma lista taxonómica preliminar dos nematodes marinhos de vida livre de 21 locais intertidais e subtidais de praias arenosas ao longo da costa da ilha de São Miguel, no arquipélago dos Açores, Portugal. A fauna de nematodes obtida encontrou-se representada por 4 ordens, 21 famílias e 43 géneros. Os géneros Cyatholaimus, Desmodora e Daptonema apresentaram 2 morfoespécies cada. A ordem Enoplida representou-se por 8 famílias e 13 géneros, Chromadorida por 7 familias e 18 géneros, a última correspondendo ao grupo de nematodes mais diverso. Monhysterida apresentou 5 famílias e 10 géneros e Araeolaimida estava representada por uma única família e 2 géneros. O género mais comum (contribuindo para 75% de todos os organismos amostrados) incluiu Adoncholaimus (o género mais abundante, 32 especímenes), Axonolaimus (18), Cyatholaimus (17), Enoploides (13), Rhabdocoma, e Acanthopharynx (11). Viscosia e Enoplolaimus foram representados por 7 especímenes, enquanto que Halalaimus, Desmoscolex, Monophostia, Daptonema, e Theristus foram representados por apenas 6 indivíduos cada. Os taxa dominates de nematodes marinhos na ilha de São Miguel têm sido comumente reportados para outros habitats costeiros incluindo praias arenosas. Podem ser considerados um componente típico da meiofauna de praias arenosas intertidais. Muitos dos morfotipos de nematodes marinhos encontrados na ilha de São Miguel podem representar novas espécies para a ciência. Tanto quanto sabemos, este é o primeiro registo de nematodes marinhos para a ilha de São Miguel e a primeira lista de nematos marinhos de baixa profundidade para os Açores. Estes resultados servirão como uma baseline importante para futuras investigações com o objectivo de melhorar a nossa compreensão sobre as bioRxiv preprint doi: https://doi.org/10.1101/2020.09.09.289918; this version posted September 10, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. comunidades de nematodes em ilhas vulcânicas como a ilha de São Miguel no arquipélago dos Açores. Palavras chave: nematodes marinhos de vida livre, meiofauna, habitats bentónicos intertidais, sedimentos vulcânicos. Introduction Shallow marine environments such as sandy beaches are among the most appreciated ecosystems by humankind not only for their recreational and economic value but also for the contribution of ecosystem services they provide like: sediment storage and transport, wave dissipation and habitat for benthic organisms (Short, 1996; McLachlan & Brown, 2006). The very condition of sandy beaches makes them look like lifeless habitats, in terms of macrofauna, however, these environments are home to a diverse and abundant interstitial fauna composed mainly by meiofauna; animals smaller than 500 µm and larger than 35 µm (McLachlan & Jaramillo 1995; Giere, 2009). Free-living nematodes are one of the most abundant meiofaunal organisms in sedimentary environments (>80% of total community abundance), where they play a pivotal role in the recycling of organic matter and energy flow, thus acting as a link between the microfauna and the benthic macrofauna as well as higher trophic groups (e.g. fishes; Bhadury et al., 2015). Nematodes are considered ubiquitous and are found in almost all environments (Heip et al., 1985), where their spatial distribution and abundance levels are often shaped by several environmental factors. However, sediment type plays a fundamental role in nematode distribution. Previous studies have shown that some nematode families such as Desmodoridae, Microlaimidae, Camacolaimidae, and Ironidae are often dominant in sandy substrates, while in finer sediments such as silts or clays, Anoplostomidae, Comesomatidae, and Linhomoeidae are usually the dominant ones (Sharma & Webster, 1983; Gourbault & Warwick, 1994; Nicholas & bioRxiv preprint doi: https://doi.org/10.1101/2020.09.09.289918; this version posted September 10, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC-ND 4.0 International license. Hodda 1999; Gheskiere et al., 2004; Urban-Malinga et al., 2004; Calles et al., 2005; Hourston et al., 2005; Moreno et al., 2006; de Jesús-Navarrete, 2007; Mundo-Ocampo et al., 2007; Bhadury et al., 2015). It is recognized that research on marine nematodes at European coastal habitats is well advanced with a better understanding of their spatio-temporal patterns, including taxonomic keys for marine nematodes from that region (Platt & Warwick, 1983; 1988;